tx & VP ctx and tests refactors #794

Job	Run time
lints	5m 52s
build-wasm (wasm, build-wasm-scripts, wasm/tx_.wasm wasm/vp_.wasm wasm/checksums.json )	4m 44s
build-wasm (wasm-for-tests, build-wasm-tests-scripts, wasm_for_tests/*.wasm)	3m 52s
build-binaries	10m 21s
check-packages	6m 1s
rust-docs	7m 0s
changelog	0s
test-unit	9m 22s
test-wasm	1m 7s
test-integration	8m 11s
check-benchmarks	0s
test-e2e	0s
upload-coverage	1s
	56m 31s

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